Small anisotropy, weak thermal fluctuations, and high field superconductivity in Co-doped iron pnictide Ba(Fe1-xCox)2As2

TL;DR

This study investigates the high-field superconducting properties of Co-doped Ba(Fe1-xCox)2As2, revealing low anisotropy, stable resistive transitions, and strong nano-structure pinning, contributing to understanding iron pnictide superconductors.

Contribution

It provides detailed high-field measurements showing low anisotropy and strong pinning in Ba(Fe1-xCox)2As2, highlighting differences from cuprates and oxypnictides.

Findings

Resistive transitions show minimal broadening up to 45 T.

Mass anisotropy decreases from ~2 near Tc to ~1.5 at lower temperatures.

Unusual symmetric pinning force curve indicates strong nano-structure pinning.

Abstract

We performed high-field magnetotransport and magnetization measurements on a single crystal of the 122-phase iron pnictide Ba(Fe1-xCox)2As2. Unlike the HTS cuprates and 1111-phase oxypnictides, Ba(Fe1-xCox)2As2 showed practically no broadening of the resistive transitions under magnetic fields up to 45 T. The mass anisotropy gamma = Hc2ab/Hc2c deduced from the slopes of the upper critical field dHc2ab/dT = 4.9T/K and dHc2c/dT = 2.5T/K decreases from ~2 near Tc, to ~1.5 at lower temperatures. We observed the irreversibility field close to Hc2, and a rather unusual symmetric volume pinning force curve Fp(H) suggestive of strong pinning nano-structure.